This invention relates, in general, to the field of high voltage, high energy capacitor discharge devices and, more particularly, to their use with electronic safe and arming devices.
Capacitor discharge devices have been employed in various electronic devices including safe and arm devices, laser firing systems and plasma generators. While the present invention will be described in the environment of a detonator for safe and arm system explosive, it will be understood that the invention is suitable for use in any application in which a high power capacitor discharge device is desired. In electronic safe and arm devices a capacitor is utilized to provide a high energy pulse to a load, e.g. a foil or film detonator. The energy pulse when coupled with a foil detonator, vaporizes the foil to initiate an explosion and one such system is described in U.S. Pat. No. 4,602,565 ('565 patent). In a typical prior art capacitor discharge system, such as in the '565 patent, the capacitor is in a circuit with the foil detonator and a normally open switch, and the capacitor is normally in an uncharged state. When it is desired to arm the system, the capacitor is charged, e.g., to 3000 volts; when it is desired to initiate the explosion, the switch is closed and the capacitor discharges very quickly (in nanoseconds) to vaporize the foil and initiate the explosion. A high resistance bleed resistor connected across the capacitor is used to bleed off the charge on the capacitor in the event that the latter is charged (i.e., armed) but then not discharged into the load if a decision is made not to "fire" a system after it has been "armed". The voltage drops across the bleed resistors is monitored to determine whether the system is armed or safe. Prior art structures for connecting the capacitor and bleed resistor together included conventional devices such as a flexible or rigid printed wire board. A problem with such prior art structures is that occasionally the bleed resistor may become electrically disconnected from the circuit. This problem is particularly serious when such a disconnection occurs while the capacitor is charged. In that structure the voltage drop across the bleed resistor is zero, indicating a safe system when, in fact, the capacitor may be charged and in an armed state. That is a very dangerous situation in that the system appears to be safe, but it is not. Closure of the switch in this situation will lead to the catastrophic result of an unintended firing of the system (explosive charge, bomb, etc.).
Another problem with prior art system is that after a failure in the connection between the bleed resistor and the capacitor, a safe (i.e., uncharged) capacitor can still be charged (i.e., armed), and the system can be fired by closure of the switch. This is a second unsafe and very dangerous condition.